U.S. patent application number 10/661535 was filed with the patent office on 2004-07-01 for method for driving plasma display panel and plasma display device.
This patent application is currently assigned to FUJITSU HITACHI PLASMA DISPLAY LIMITED. Invention is credited to Hirakawa, Hitoshi, Kanazawa, Yoshikazu, Nishimura, Satoru, Shiizaki, Takashi, Tanaka, Shinsuke.
Application Number | 20040125051 10/661535 |
Document ID | / |
Family ID | 32463644 |
Filed Date | 2004-07-01 |
United States Patent
Application |
20040125051 |
Kind Code |
A1 |
Hirakawa, Hitoshi ; et
al. |
July 1, 2004 |
Method for driving plasma display panel and plasma display
device
Abstract
A method for driving a plasma display panel, wherein a display
field, corresponding to a display of a screen, is composed of a
plurality of subfields, a gradation display is realized by
combining subfields to be lit among the plurality of subfields,
cells to be lit in the display field are separated from unlit cells
and all of the cells to be lit are lit in a predetermined subfield
arranged near the head in the display field. The gradation display
level is set with the light emission in the predetermined subfield
being taken into consideration.
Inventors: |
Hirakawa, Hitoshi;
(Kawasaki, JP) ; Tanaka, Shinsuke; (Kawasaki,
JP) ; Shiizaki, Takashi; (Kawasaki, JP) ;
Nishimura, Satoru; (Kawasaki, JP) ; Kanazawa,
Yoshikazu; (Kawasaki, JP) |
Correspondence
Address: |
STAAS & HALSEY LLP
SUITE 700
1201 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
FUJITSU HITACHI PLASMA DISPLAY
LIMITED
Kawasaki
JP
|
Family ID: |
32463644 |
Appl. No.: |
10/661535 |
Filed: |
September 15, 2003 |
Current U.S.
Class: |
345/63 |
Current CPC
Class: |
G09G 3/2033 20130101;
G09G 3/2927 20130101; G09G 3/291 20130101; G09G 2320/0238 20130101;
G09G 3/2037 20130101; G09G 2320/066 20130101 |
Class at
Publication: |
345/063 |
International
Class: |
G09G 003/28 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2002 |
JP |
2002-380904 |
Claims
We claim:
1. A method for driving a plasma display panel, wherein a display
field, corresponding to a display of a screen, is composed of a
plurality of subfields, a gradation display is realized by
combining subfields to be lit among the plurality of subfields,
each subfield comprises at least an address period to write cells
to be lit in the subfield and a sustain period to cause light
emission to occur in the written cells, and all of the cells to be
lit in a display field are lit in a predetermined subfield among
the plurality of subfields making up the display field.
2. A method for driving a plasma display panel, as set forth in
claim 1, wherein the predetermined subfield is a subfield with the
lowest luminance ratio.
3. A method for driving a plasma display panel, as set forth in
claim 1, wherein a display field has a subfield with a same
luminance ratio as that of the predetermined subfield, in addition
to the predetermined subfield.
4. A method for driving a plasma display panel, as set forth in
claim 1, wherein the predetermined subfield is the subfield at the
head in a display field.
5. A method for driving a plasma display panel, as set forth in
claim 1, wherein an all-cell write discharge is caused to occur in
the predetermined subfield before the address period.
6. A method for driving a plasma display panel, as set forth in
claim 1, wherein an all-cell write discharge is caused to occur in
the predetermined subfield and a subfield with a heavy weight of
luminance before the address period.
7. A method for driving a plasma display panel, as set forth in
claim 5, wherein the all-cell write discharge is caused to occur
twice successively in the predetermined subfield.
8. A method for driving a plasma display panel, as set forth in
claim 5, wherein a subfield reset discharge is caused to occur in
order to erase the residual charges in a lit cell in the subfield
immediately before the subfield in which the all-cell write
discharge is caused to occur.
9. A method for driving a plasma display panel, as set forth in
claim 1, wherein the subfield with the lowest luminance ratio is
arranged at the head in a display field and the predetermined
subfield is arranged in the second position in the display
field.
10. A method for driving a plasma display panel, as set forth in
claim 9, wherein the predetermined subfield is one with the second
lowest luminance ratio.
11. A method for driving a plasma display panel, as set forth in
claim 9, wherein an all-cell write discharge is caused to occur in
the subfield at the head and the predetermined subfield before the
address period.
12. A method for driving a plasma display panel, as set forth in
claim 9, wherein a subfield reset discharge is caused to occur in
order to erase the residual charges in a lit cell in the subfield
at the head.
13. A method for driving a plasma display panel, as set forth in
claim 1, wherein the widths of an address pulse and a scan pulse
during the address period in the predetermined subfield are wider
than those of the address pulse and the scan pulse during the
address period in other subfields.
14. A method for driving a plasma display panel, as set forth in
claim 1, wherein the voltage of an address pulse during the address
period in the predetermined subfield is greater than that of the
address pulse during the address period in other subfields.
15. A method for driving a plasma display panel, as set forth in
claim 1, wherein the voltage of a scan pulse during the address
period in the predetermined subfield is greater than that of the
scan pulse during the address period in other subfields.
16. A method for driving a plasma display panel, as set forth in
claim 1, wherein a process to suppress a discharge in an unlit cell
is performed between the address period and the sustain period in
the predetermined subfield.
17. A method for driving a plasma display panel, as set forth in
claim 16, wherein the process to suppress a discharge in an unlit
cell is a process in which, at the same time an address pulse is
applied to an address electrode, a pulse, the applied voltage of
which varies as time elapses, is applied to a scan electrode.
18. A method for driving a plasma display panel, as set forth in
claim 17, wherein the final potential of the pulse, the applied
voltage of which varies as time elapses, is lower than the finally
reached potential of a charge control pulse, which is applied after
an all-cell write discharge and the applied voltage of which varies
as time elapses.
19. A method for driving a plasma display panel, as set forth in
claim 1, wherein the gradation display level is determined with the
luminance due to lighting in the predetermined subfield being taken
into consideration.
20. A plasma display device comprising a plasma display panel and a
driving circuit for the plasma display panel, wherein the driving
circuit drives the plasma display panel using the driving methods
set forth in claim 1.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a method for driving a
plasma display panel (PDP) and a PDP device. More particularly, the
present invention relates to a driving method that improves the
display contrast of a PDP.
[0002] FIG. 1 is a diagram showing a basic configuration of a PDP
device.
[0003] A plasma display panel (PDP) 1 is a device in which a
discharge space sandwiched by two glass substrates filled up with a
mixture of neon gas, xenon gas, etc., a discharge is occurred by
applying a voltage greater than a discharge start voltage between
electrodes formed on the substrate, and phosphors formed on the
substrate are excited so that they emit light due to ultraviolet
rays generated by the discharge. Although various configurations
have been proposed for a PDP, an AC type/three-electrode surface
discharge type panel, which is currently most widely used, is
described as an example.
[0004] In the plasma display panel (PDP) 1, a plurality of X
electrodes (sustain electrode) 2 and a plurality of Y electrodes
(scan electrode) 3 are arranged adjacently by turn and a plurality
of address electrodes (third electrodes) 4 are arranged in the
direction perpendicular to that in which the X electrodes and the Y
electrodes extend. Between a pair of X electrode and Y electrode,
that is, between X1 and Y1, between X2 and Y2, . . . , a display
line is formed and a display cell 5 is formed at the crossing of
each display line and the address electrode 4. The X electrodes and
the Y electrodes are referred to as the display electrodes.
[0005] The X electrodes are commonly connected to an X drive
circuit 7 and the same drive signal is applied all to them. The X
drive circuit 7 is provided with a sustain pulse circuit 8 that
generates a sustain pulse, and a reset/address voltage generation
circuit 9 that generates a voltage used during the reset and
address operations, both of which will be described later. The Y
electrodes are connected individually to a scan circuit 11 provided
within a Y drive circuit 10, and a scan pulse is applied
sequentially to them during an address period which will be
described later. The Y drive circuit 10 is further provided with a
sustain pulse circuit 12 that generates a sustain pulse, and a
reset/address voltage generation circuit 13 that generates a
reset/address voltage. The address electrodes are connected to an
address driver 6 and an address signal to select a cell to be lit
or not to be lit is applied to them during the address operation in
synchronization with the scan pulse.
[0006] As a discharge in a PDP takes only two values, that is, ON
and OFF, gradation is displayed by varying the number of times of
light emission. Therefore, one display field that corresponds to a
display of a screen is divided into a plurality of subfields. Each
subfield is composed of a reset period, an address period and a
sustain discharge period (sustain period). During the reset period,
the reset operation is performed so that all of the display cells
are put into a uniform state in which, for example, wall charges
are erased, or wall charges are formed uniformly, regardless of the
lit or unlit state of the cells in the previous subfield. During
the address period, a selective discharge (address discharge) is
caused to occur so that the ON (lit) or OFF (unlit) state of a
display cell is determined according to display data and the wall
charges in a cell to be lit are put into a state different from
that of a cell not to be lit. During the sustain period, a
discharge is caused to occur repeatedly in a display cell selected
during the address period and light is emitted. If the number of
sustain discharge pulses, that is, the period of the sustain
discharge pulse, is constant, the length of the sustain discharge
period differs from subfield to subfield, therefore gradation can
be displayed by setting the ratio of times of light emission in
each subfield to, for example, 1:2:4:8: . . . , and combining
subfields that are to emit light according to the gradation of each
display cell.
[0007] FIG. 3 is a diagram that shows typical examples of drive
waveforms in each subfield of a conventional PDP device. As shown
schematically, during the reset period, in a state in which 0V is
being applied to an address electrode A, an inclined wave-shaped
pulse m, the voltage of which varies gradually from 0V to Vs+Vw, is
applied to the Y electrode, and an inclined wave-shaped pulse, the
voltage of which gradually varies from 0V to -Vs, is applied to the
X electrode. Due to this, a discharge is caused to occur in all of
the cells regardless of the wall charges accumulated in the display
cell, and negative wall charges are accumulated on the Y electrode
and the positive charges, on the X electrode. This is called the
all-cell write discharge (reset discharge). Subsequently to this,
an inclined wave-shaped charge control pulse n, the voltage of
which drops gradually from Vs, is applied to the Y electrode and a
voltage Vs is applied to the X electrode, therefore, the wall
charges accumulated in the Y electrode and X electrode by the write
discharge decrease almost to zero. Although a description is given
below using an example of an inclined wave-shaped pulse, the
voltage of which varies linearly, it is possible for there to be a
case where the voltage does not vary linearly.
[0008] During the address period, the voltage Vx is applied to the
X electrode and, in a state in which 0V is being applied to the Y
electrode, a scan pulse having a voltage -Vs-Vy is applied
sequentially to the Y electrode and an address voltage Va is
applied to the address electrode A in a cell to be lit in
synchronization with the application of the scan pulse. The voltage
0V is applied to the address electrode in a cell not to be lit. An
address discharge is caused to occur in a cell to be lit to which
the scan pulse and the address voltage have been applied, and
positive wall charges are accumulated in the Y electrode and
negative charges are accumulated in the X electrode. In this case,
the quantities of these wall charges in the Y electrode and X
electrode are sufficient to cause a sustain discharge to occur when
a sustain discharge pulse is applied. As an address discharge is
not caused to occur in a cell not to be lit, the quantities of wall
charges in the Y electrode and X electrode are made to remain
almost zero.
[0009] During the sustain discharge period, in a state in which 0V
is being applied to the address electrode, the voltage Vs and the
voltage -Vs are applied alternately to the X electrode and Y
electrode as a sustain pulse. The voltage of the sustain pulse to
be applied to the Y electrode for the first time is set to Vs+Vu.
In a cell to be lit, the voltage due to wall charges is added to
the voltage of the sustain pulse, the discharge start voltage is
exceeded and a sustain discharge is caused to occur, and the
charges move and a quantity of charges necessary for the next
sustain discharge are accumulated in the Y electrode and X
electrode. In other words, when the address period is completed,
positive wall charges are accumulated in the Y electrode and
negative wall charges are accumulated in the X electrode, that is,
a voltage, the high potential side of which is the Y electrode, is
applied between the Y electrode and the X electrode. Therefore, if
the voltage Vs+Vu is applied to the Y electrode as a sustain pulse
and -Vs is applied to the X electrode at the inception of the
sustain period, the voltage due to the above-mentioned wall charges
is added so that the discharge start voltage is exceeded, and a
sustain discharge is caused to occur. When a sustain discharge is
caused to occur, the positive charges move from the Y electrode to
the X electrode and accumulate therein, the negative charges move
from the X electrode to the Y electrode and accumulate therein, and
the sustain discharge is terminated because a voltage, the high
potential side of which is the X electrode, is produced by the
movement of charges. Then, if -Vs is applied to the Y electrode as
a sustain pulse and the voltage Vs is applied to the X electrode, a
sustain discharge is caused to occur because the voltage due to the
wall charges, the high potential side of which is the x electrode,
is added. This cycle is repeated during the sustain period. As no
charge is accumulated in a cell not to be lit, no discharge is
caused to occur even though a sustain pulse is applied to either
electrode.
[0010] Each subfield has a structure as described above, but the
length of the sustain period, that is, the number of sustain
pulses, differs according to the weights of luminance in each
subfield. A desired gradation can be displayed by combining
subfields to be lit from among ten subfields.
[0011] FIG. 4 is a diagram that shows an example of gradation
display in a conventional PDP device. In this example, one display
field is composed of ten subfields SF1-SF10 and each subfield has a
luminance ratio as shown schematically. At the head of the one
display field, SF1 with the lowest luminance ratio is arranged and
following this, the subfields each having each luminance ratio
shown schematically are arranged in order. When each gradation
level is displayed, subfields to be lit are combined as shown
schematically. Although only the gradation levels 0 to 35 are shown
here, it is possible to display up to 124 gradation levels in this
example. Moreover, in this example, by providing subfields having
the same luminance ratio in twos for the four kinds of luminance
ratios, it is possible for there to be multiple combinations for
the display of the same gradation level. Due to this, a color false
contour can be reduced.
[0012] A description has been given of the conventionally typical
PDP device as above, but it is possible for there to be various
methods for the PDP device. For example, Japanese Unexamined Patent
Publication (Kokai) No. 9-160525 has disclosed a PDP device in
which the number of display lines is doubled while the number of
sustain electrodes remains the same as conventionally, by utilizing
all the gaps between neighboring sustain electrodes as a display
cell. Although it is possible to apply the present invention to any
PDP device as long as it displays gradation using the subfield
method, no further description is given here.
[0013] In an AC type PDP device, the quantity or the state of
accumulated wall charges in a cell after the sustain period differs
between a cell to be lit and one not to be lit. Therefore, there is
a problem that the address discharge in the subsequent subfield
becomes unstable and it is difficult to ensure a sufficient
operation margin. In an AC type PDP device, therefore, the all-cell
write discharge (reset discharge) is caused to occur during the
reset period in each subfield as described above, and the wall
charges in each cell are brought into a uniform state. However, as
the all-cell write discharge is caused to occur in all of the
cells, even a cell not to be lit is made to light and as a result,
a problem occurs that the background luminance becomes high and the
contrast ratio is lowered significantly.
[0014] Therefore, there have been proposed various driving methods
for improving the contrast ratio.
[0015] Japanese Unexamined Patent Publication (Kokai) No.
2000-75835 has disclosed a driving method for improving the
contrast ratio in which the intensity of discharge during the reset
period is reduced by using a pulse to be applied to the Y electrode
during the reset period, which is wave-shaped and the voltage of
which varies gradually.
[0016] Japanese Unexamined Patent Publication (Kokai) No. 5-313598
has disclosed a driving method in which the all-cell write
discharge is caused to occur only in the subfield at the head in a
display field and the all-cell write discharge is not caused to
occur in other subfields. Due to this, the contrast ratio is
improved because the number of times the all-cell write discharge
is caused to occur is reduced.
[0017] Japanese Unexamined Patent Publication (Kokai) No. 3-219286
has disclosed a driving method in which a preliminary discharge
subfield is provided and a preliminary discharge is caused to occur
in all of the cells.
[0018] Japanese Unexamined Patent Publication (Kokai) No.
2002-72961 has disclosed a driving method in which a subfield for
resetting is provided at the head in a display subfield and a reset
discharge is caused to occur in the subfield for resetting for a
cell that is to emit light.
[0019] The most effective driving method for improving the contrast
ratio among the prior arts is that which has been disclosed in
Japanese Unexamined Patent Publication (Kokai) No. 2000-75835, in
which a reset discharge (all-cell write discharge) is caused to
occur only in the subfield at the head and it is not caused to
occur in other subfields. However, this driving method has the
following problems.
[0020] (1) When the all-cell write discharge is caused to occur
only in the subfield at the head, it is necessary to raise the
write voltage to greater than that used in a case where a reset
discharge is caused to occur in all of the subfields because the
time interval from this discharge until the address discharge is
lengthened in subsequent subfields, therefore, the cost of a drive
circuit is raised, the amount of increment in the background
luminance due to one reset discharge becomes large, and the
contrast ratio is not reduced sufficiently.
[0021] (2) In the second and subsequent subfields, wall charges
formed by the sustain discharge are formed in a cell that has been
lit in the previous subfield but, in an unlit cell, only wall
charges formed by the reset discharge in the subfield at the head
are formed and, therefore, the states of wall charges are
different. Due to this, if an address discharge is caused to occur
in these states, a problem occurs that the address discharge
becomes unstable in some cells and it is difficult to ensure the
operation margin.
[0022] (3) Although an address discharge is caused to occur in each
subfield by utilizing the wall charges formed by the reset
discharge caused to occur in the subfield at the head, the priming
effect diminishes in a cell where an unlit subfield follows another
because the time interval, from the formation of the wall charges
in the subfield at the head until they are utilized, is lengthened.
Therefore, in a cell that is lit for the first time in a subfield
near the end, a problem occurs that it is unlikely that the address
discharge is caused to occur normally. Moreover, it is necessary to
raise the address voltage in order to solve this problem, and as a
result, the cost of the drive circuit is increased.
[0023] (4) A sustain discharge exerts influence also on the
surrounding unlit cells through the discharge diffusion. Therefore,
it is difficult to maintain the wall charges in the unlit cells
formed by the reset discharge in the subfield at the head, and the
next reset discharge is affected. Therefore, it is necessary to
widen the reverse slit by increase the distance between neighboring
cells or to design so that a partition (rib) is provided between
cells, but this will degrade the display luminance of the panel.
Moreover, it is impossible to widen the reverse slit in the case of
the ALIS method disclosed in the above-mentioned Japanese
Unexamined Paten Publication (Kokai) No. 9-160525, in which all of
the spaces between sustain electrodes are used as a cell.
[0024] Because of the above-mentioned problems, it is, therefore,
difficult to apply the driving method, in which a reset discharge
is caused to occur only in the subfield at the head, to a
high-resolution PDP device in which the reverse slit cannot be
widened. Moreover, a PDP device having a box rib structure is free
from the above-mentioned problems (3) and (4), but it is necessary
to raise the write voltage because cells are enclosed by ribs and
completely separate from each other, therefore, the cost of the
drive circuit is increased.
SUMMARY OF THE INVENTION
[0025] The object of the present invention is to realize a driving
method able to realize a high-contrast PDP device that is free from
the above-mentioned problems.
[0026] In order to realize the above-mentioned object, the method
for driving a plasma display panel according to the present
invention is characterized in that cells to be lit are separated
from cells not to be lit in a display field and all of the cells to
be lit are lit in a predetermined subfield arranged at a position
near the head in the display field. The gradation level is set with
the light emission in the predetermined subfield being taken into
consideration.
[0027] FIG. 5 is a diagram that illustrates the principle of the
present invention. It is assumed that subfields SF1, SF2, SF3, SF4,
. . . , are arranged in this order in a display field.
Conventionally, each subfield is combined to display a
predetermined gradation level, and in some cases, a cell that is
not lit in the subfield SF1 at the head is lit in a subsequent
subfield. Contrary to this, in the configuration according to the
present invention, whenever there is a subfield to be lit in a
display field, it is always lit in the subfield SF1 at the head. A
reset discharge is caused to occur only in a predetermined subfield
and not in other subfields, but it is possible for there to be a
modification such as that a reset discharge is caused to occur in a
subfield with a large luminance ratio, as will be described later.
Due to this, the contrast ratio can be improved similar to the
conventional case where a reset discharge is caused to occur only
in the subfield at the head and the following advantages can be
expected.
[0028] (1) As the wall charges formed by a sustain discharge are
more stable than those formed by a reset discharge (write
discharge), the above-mentioned problems relating to the prior art
do not occur. For example, when a cell is lit in a subfield after
the predetermined subfield, a high write voltage (reset voltage) is
not required because a cell in which an address discharge is caused
to occur uses the wall charges formed by a sustain discharge.
[0029] In the conventional case shown in FIG. 5, for example, the
cell in the fourth row and second column is lit in SF4 for the
first time. Therefore, the wall charges formed by the reset
discharge in SF1 are used. Contrary to this, in the present
invention, the cell in the fourth row and second column has been
lit in SF1 and when it is lit in SF4, the wall charges formed by
the sustain discharge are used.
[0030] (2) Because the lit cells are completely separated from the
unlit cells in a display field, it is possible to bring wall
charges into a desired state, individually, by a proper process and
to ensure an operation margin for a stable operation.
[0031] (3) Both the priming effects of the write discharge (reset
discharge) and the sustain discharge can be used.
[0032] As described above, the method for driving a plasma display
panel according to the present invention can improve the contrast
ratio as the conventional driving method can do and at the same
time, it can solve the problems relating to the prior art.
[0033] A fixed subfield is, for example, a subfield with the lowest
luminance ratio, and in this case, the predetermined subfield is
arranged at the head. It is also possible to arrange a subfield
with the lowest luminance ratio at the head and a subfield with the
second lowest luminance ratio at the second position, and use the
second subfield as a fixed subfield, and thus there can be various
modifications.
[0034] It is desirable to provide, in addition to a predetermined
subfield, a subfield having the same luminance ratio as the
predetermined subfield in a display field. Due to this, if, for
example, the subfield with the lowest luminance ratio is the
predetermined subfield, it is possible to display any gradation
level by combining the subfields which light the predetermined
subfield.
[0035] In the predetermined subfield, it is desirable to provide a
reset period, during which the all-cell write discharge is caused
to occur, before an address period. It is also desirable to provide
a reset period, during which the all-cell write discharge is caused
to occur, before an address period, not only in the predetermined
subfield but also in a subfield with a heavy weight of luminance.
Moreover, when the predetermined subfield is arranged at the second
position, it is desirable to provide a reset period in the subfield
at the head with the lowest luminance ratio. It is not necessary to
provide a reset period in other subfields. During the reset period,
the all-cell write discharge can be caused to occur twice or more
successively.
[0036] It is desirable to cause a subfield reset discharge to occur
to erase the residual charges in a lit cell in a subfield
immediately before a subfield having a reset period.
[0037] In the predetermined subfield, it is desirable to widen the
width of the address pulse in the address period so that the width
is wider than that of the address pulse in other subfields, to
raise the voltage of the address pulse so that the voltage is
greater than that of the address pulse in other subfields, or to
raise the voltage of the scan pulse so that the voltage is greater
than that of the scan pulse in other subfields.
[0038] Moreover, in the predetermined subfield, it is desirable to
perform a process to suppress the discharge in an unlit cell
between the address period and the sustain period. This process is,
for example, a process in which an address pulse is applied to the
address electrode and at the same time, an inclined wave-shaped
pulse is applied to the scan electrode. In this case, the final
potential of the inclined wave-shaped pulse is set so as to be
lower than the finally reached potential of an inclined wave-shaped
charge control pulse during the reset period.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] The features and advantages of the present invention will be
more clearly understood from the following description taken in
conjunction with the accompanying drawings in which:
[0040] FIG. 1 is a general configuration diagram of a plasma
display (PDP) device;
[0041] FIG. 2 is a diagram that shows the configuration of a
display field according to the subfield method;
[0042] FIG. 3 is a diagram that shows examples of conventional
drive waveforms;
[0043] FIG. 4 is a diagram that shows the combination of subfields
for a conventional gradation display;
[0044] FIG. 5 is a diagram that illustrates the principle of the
present invention;
[0045] FIG. 6 is diagram that shows the combination of subfields
for a gradation display in a first embodiment of the present
invention;
[0046] FIG. 7 is a diagram that shows drive waveforms in SF1 and
SF2 in the first embodiment;
[0047] FIG. 8 is a diagram that shows the combination of subfields
for a gradation display in a second embodiment of the present
invention;
[0048] FIG. 9 is a diagram that shows drive waveforms in SF1, SF2
and SF3 in the second embodiment;
[0049] FIG. 10 is a diagram that shows a modification of the drive
waveforms in the first embodiment; and
[0050] FIG. 11 is a diagram that shows another modification of the
drive waveforms in the first embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0051] The PDP device in the embodiments of the present invention
has a configuration as shown in FIG. 1. However, the present
invention is not limited to this, but can be applied to any PDP
device as long as it realizes gradation display by the subfield
method, for example, the PDP device using the ALIS method disclosed
in Japanese Unexamined Patent Publication (Kokai) No. 9-160525.
[0052] FIG. 6 is a diagram that shows the configuration of
subfields and the combination that realizes the gradation level in
the PDP device in the first embodiment of the present invention.
Although only the gradation levels from 0 to 35 are shown here, it
is possible to realize the gradation levels from 0 to 124 with this
configuration. As is obvious by comparison with FIG. 4, the
configuration of subfields in the first embodiment differs from
that in the conventional case in that a subfield with luminance
ratio 1 is added at the head of the subfield configuration.
Therefore, there are provided, as a result, two subfields with
luminance ratio 1. The second subfield SF2 with luminance ratio 1
can be arranged in another position.
[0053] As shown schematically, the subfield SF1 at the head is lit
when any gradation level equal to 1 or higher is displayed. Even
though SF1 is always lit as described above, it is possible to
display any gradation level because there are two subfields with
luminance ratio 1. In the conventional case, SF1 is lit only when
an odd-numbered gradation level is displayed, and SF1 is not lit
when an even-numbered gradation level is displayed. Contrary to
this, it is possible, in the present embodiment, to light SF1 at
the head when an odd-numbered gradation level is displayed as
similar to the conventional case and always to light SF1 when an
even-numbered gradation level is displayed by the combination with
SF2 with luminance ratio 1 for display. For example, when the
gradation level 2 is displayed, both SF1 and SF2 are lit and when
the gradation level 4 is displayed, SF1, SF2 and SF7 (luminance
ratio 2) are lit. Moreover, when the gradation level 32 is
displayed, SF1, SF2 and SF4 to SF7 are lit. Therefore, all of the
cells that are to be lit in SF2 and subsequent subfields are only
those that are lit in SF1.
[0054] FIG. 7 is a diagram that shows the drive waveforms in SF1
and SF2 and subsequent subfields in the first embodiment. In SF1,
as shown schematically, the reset period is provided, as is similar
to the conventional case shown in FIG. 3, and the all-cell write
discharge (reset discharge) is caused to occur, then the inclined
wave-shaped charge control pulse is applied for the adjustment of
wall charges. Subsequently to this, an address discharge is caused
to occur in a cell to be lit in the address period and wall charges
necessary for the sustain discharge are formed. Moreover, during a
period NE, in a state in which 0V is being applied to the X
electrode and Va is being applied to the address electrode, an
inclined waveform p, the voltage of which varies from 0V to -Vs, is
applied to the Y electrode, and the quantity of wall charges in an
unselected cell are adjusted to a proper value. Then, Vs and -Vs
are applied alternately to the Y electrode and the X electrode
during the sustain period and a sustain discharge is caused to
occur (the first pulse is Vs+vu).
[0055] In SF2, the all-cell write discharge, which has been caused
to occur in SF1 during the sustain period, is not caused to occur,
but only the inclined wave-shaped charge control pulse is applied
and the period NE is not provided. The subsequent subfields are the
same as SF2 only with exception of the length of the sustain
period.
[0056] By using these drive waveforms, it is possible to cause an
address discharge to occur even if a write discharge is not caused
to occur, because all of the cells to be lit in SF2 and subsequent
subfields have been lit in SF1 and have wall charges formed by the
sustain discharge in SF1. Therefore, the number of times of write
discharges (reset discharge) is reduced and the contrast is
improved.
[0057] Moreover, in SF2 and subsequent subfields, as the address
discharge is caused to occur by using the wall charges formed by
the sustain discharge in SF1, it is not necessary to raise the
voltage of the write discharge in SF1 greater than that required.
As described above, in the conventional case where the all-cell
write discharge is caused to occur in SF1, the time interval from
the all-cell write discharge in SF1 until the address discharge is
caused to occur in a subsequent subfield is lengthened, therefore,
it is necessary to raise the voltage of the all-cell write
discharge in SF1 to greater than that in the case where the
all-cell write discharge is caused to occur in all of the
subfields. Contrary to this, in the present embodiment, as the wall
charges formed by the sustain discharge in SF1 are used, the
voltage of the write discharge in SF1 can be almost equal to that
in the case where the all-cell discharge is caused to occur in all
of the subfields. Therefore, according to the present invention,
the contrast ratio can be further improved compared to the
conventional case where the all-cell write discharge is caused to
occur in SF1.
[0058] In SF1, all of the cells to be lit in the display field are
selected and the sustain discharge is caused to occur. Therefore,
the cells not to be lit in SF1 are those not to be lit in the
display field, and if the quantity of wall charges in the unlit
cells are adjusted to a proper value, it is possible to suppress
the mutual interference between cells and increase the operation
margin because the possibility of the unlit cells to erroneously
emit light in subsequent subfields is reduced. In concrete terms,
all that has to be done is to prevent a discharge from occurring
even if an address pulse and a scan pulse are applied to the unlit
cells, that is, Va is applied to the address electrode during the
period NE as described above, and the inclined waveform p, the
voltage of which varies from 0V to -Vs is applied to the Y
electrode. At this time, it is desirable to lower the finally
reached potential of the waveform p than that of the inclined
wave-shaped charge control pulse n.
[0059] FIG. 8 is a diagram that shows the configuration of
subfields and the combination of subfields to display gradation
levels in the PDP device in the second embodiment of the present
invention. Similar to FIG. 6, although only the gradation levels 0
to 67 are shown here, 0 to 247 gradation levels can be displayed
with this configuration. However, some gradation levels cannot be
displayed. As shown schematically, in the configuration of
subfields in the second embodiment, there are 11 subfields, and SF1
has the lowest luminance ratio 1, SF2 has the luminance ratio 2,
and the subfields having the luminance ratios 64, 32, 16, 8, 4, 8,
16, 32 and 64 are arranged in this order. As shown schematically,
the second SF2 is lit when all of the gradation levels equal to 2
or higher are displayed. Therefore neither the gradation level 4
nor 5 can be displayed.
[0060] FIG. 9 is the diagram that shows the drive waveforms in SF1,
SF2 and subsequent subfields in the second embodiment. As shown
schematically, the waveforms in SF1 are provided with the reset
period, the address period, the sustain period, and an SF reset
period R. The reset period, the address period and the sustain
period are the same as the drive waveforms in the conventional case
shown in FIG. 3. In the SF reset period R, a negative pulse (-Vs)
is applied to the Y electrode to erase the residual charges formed
by the sustain discharge in the lit cells.
[0061] The drive waveforms in SF2 are the same as the drive
waveforms in SF1 in the first embodiment and the drive waveforms in
SF3 and subsequent subfields are the same as the drive waveforms in
SF2 and subsequent subfields in the first embodiment.
[0062] In the second embodiment, all of the cells to be lit in a
display field have been lit in SF2, therefore, it is not necessary
to cause the all-cell write discharge to occur in SF3 and
subsequent subfields as is similar to the first embodiment. In the
second embodiment, the all-cell write discharge is caused to occur
in SF1 and SF2, therefore, the contrast ratio is lowered
accordingly but improved compared to the conventional case. As
described above, it is possible for there to be various
modifications of the present invention that will bring advantages,
although there are some defects.
[0063] FIG. 10 is a diagram that shows an example of modification
of the drive waveforms in the first embodiment in FIG. 6. In this
example of modification, the width of the address pulse in SF1 is
made to be wider than that in other subfields and the voltage of
the address pulse is made to be greater than that in other
subfields. Moreover, the width of the scan pulse in SF1 is made to
be wider than that in other subfields and the voltage of the scan
pulse is made to be greater than that in other subfields. Due to
this, it is possible to certainly cause an address discharge to
occur in a cell to be lit in SF1. In SF2 and subsequent subfields,
the wall charges formed by the sustain discharge in SF1 are used
and, therefore, the address discharge is certainly caused to occur
even though the widths of the address pulse and the scan pulse are
narrow and their voltages are low. Due to this, the address period
in a display filed can be shortened as a whole.
[0064] FIG. 11 is a diagram that shows another example of
modification of the drive waveforms in the first embodiment in FIG.
6. In this example of modification, the all-cell write discharge is
caused to occur twice successively and the inclined wave-shaped
charge control pulse is applied twice successively in SF1. In other
words, two reset periods are provided one after another
contiguously. This means that the all-cell write discharge is
caused to occur twice and the address discharge can be caused to
occur in SF1 more certainly.
[0065] Although the embodiments described above are those in which
the reset period is provided only in SF1 or only in SF1 and SF2, it
is possible to further provide the reset period in a subfield with
a large luminance ratio so that an address discharge can be caused
to occur in the subfield more certainly.
[0066] As described above, according to the driving method of the
present invention, it is possible to realize a PDP device of high
display quality that never produces display errors or the like even
if the number of times of all-cell write discharge is reduced to
improve the contrast ratio.
* * * * *